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Tropical Storm FLORENCE


ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM FLORENCE DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062006
500 AM EDT WED SEP 06 2006
 
A SIGNIFICANT BURST OF DEEP CONVECTION OCCURRED NORTHEAST OF THE
ESTIMATED CENTER DURING THE OVERNIGHT HOURS. HOWEVER...SINCE THE
LOW LEVEL CIRCULATION REMAINS BOTH ELONGATED AND DISPLACED TO THE
SOUTHWEST OF THE STRONGEST ACTIVITY...THIS FLARE UP DOES NOT
NECESSARILY INDICATE IMPROVED ORGANIZATION OR AN INCREASE IN
INTENSITY. INDEED...DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB
ARE UNCHANGED AT 40 KT AND A RECENT UW-CIMSS AMSU INTENSITY
ESTIMATE WAS 42 KT. BASED ON THIS DATA...THE INITIAL INTENSITY
REMAINS 40 KT.  WATER VAPOR IMAGERY SHOWS THAT THE TROUGH TO THE
NORTHWEST OF FLORENCE IS BEGINNING TO FRACTURE CAUSING THE
FORMATION OF AN UPPER LOW.  GLOBAL MODELS INDICATE THIS UPPER LOW
WILL BEGIN TO RETROGRADE OVER THE NEXT DAY OR SO CAUSING A GRADUAL
REDUCTION IN VERTICAL SHEAR AND A MORE FAVORABLE ENVIRONMENT FOR
STRENGTHENING.  HOWEVER...THIS EXPECTED EVOLUTION IS STRONGLY
DEPENDENT ON THE PHASING OF THE UPPER LOW AND THE CYCLONE.  SHOULD
FLORENCE GET TOO CLOSE TO THE UPPER LOW...VERTICAL SHEAR WOULD
LIMIT THE POTENTIAL FOR DEVELOPMENT.  ACCORDINGLY...THE INTENSITY
FORECAST REMAINS RATHER TRICKY AND A FAIR AMOUNT OF UNCERTAINTY
EXISTS.  THE OFFICIAL FORECAST ASSUMES THE VERTICAL SHEAR WILL
RELAX IN A DAY OR SO ALLOWING GRADUAL STRENGTHENING IN LINE WITH
AVAILABLE GUIDANCE. 
 
GIVEN THE RECENT INCREASE IN DEEP CONVECTION...THE CENTER OF
FLORENCE CONTINUES TO JUMP AROUND A BIT WITH THE CURRENT POSITION
INDICATING SOME RELOCATION TO THE NORTH. THE INITIAL MOTION IS
THUS BASED ON A LONGER TERM AVERAGE YIELDING 300/11.  THE TRACK
FORECAST REASONING REMAINS UNCHANGED AS GLOBAL MODELS ARE IN
EXCELLENT AGREEMENT ON THE EASTWARD MIGRATION OF A MID-LEVEL
ANTICYCLONE NORTH OF FLORENCE.  GUIDANCE IS TIGHTLY CLUSTERED ABOUT
A GENERAL WEST-NORTHWEST HEADING OVER THE NEXT 2-3 DAYS. 
THEREAFTER...A GRADUAL TURN MORE NORTHWARD IS EXPECTED AS THE
CYCLONE REACHES THE WESTERN PERIPHERY OF THE ANTICYCLONE. 
UNFORTUNATELY...THE GLOBALS CONTINUE TO SHOW DISCREPANCIES IN THE
EVOLUTION OF AN UPSTREAM SHORT-WAVE TROUGH MOVING THROUGH THE
EASTERN UNITED STATES THIS WEEKEND.  THIS RESULTS IN DIFFERENCES
AMONG THE MODELS IN THE DEGREE...TIMING...AND LOCATION OF THE
AFOREMENTIONED NORTHWARD TURN. THE MOST NOTABLE SHIFT IN GUIDANCE
FOR THIS PACKAGE IS THE UKMET AND NOGAPS MODELS...BOTH OF WHICH
HAVE SHIFTED A LITTLE TO NORTH EARLY IN THE FORECAST AND A LITTLE
EAST LATE.  GIVEN THE APPARENT NORTHWARD REFORMATION OF THE CENTER
INITIALLY...THIS SHIFT APPEARS REASONABLE AND THE OFFICIAL FORECAST
FOLLOWS SUIT.  THE NEW FORECAST TRACK IS STILL ON THE LEFT SIDE OF
GUIDANCE ENVELOP. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      06/0900Z 18.4N  50.2W    40 KT
 12HR VT     06/1800Z 19.2N  51.6W    45 KT
 24HR VT     07/0600Z 20.3N  53.4W    55 KT
 36HR VT     07/1800Z 21.4N  55.5W    60 KT
 48HR VT     08/0600Z 22.4N  57.8W    65 KT
 72HR VT     09/0600Z 24.4N  62.6W    75 KT
 96HR VT     10/0600Z 27.0N  66.5W    85 KT
120HR VT     11/0600Z 29.5N  68.0W    95 KT
 
$$
FORECASTER RHOME/BEVEN
 
NNNN


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Page last modified: Monday, 11-Sep-2006 11:28:37 UTC